Factor completely. $36c^2-84cd+49d^2=$
Answer: $\begin{aligned} &\phantom{=}36 c ^2 - 84 c d + 49 d ^2 \\\\ &= ({6 c })^2 - 2({6 c })({7 d })+({7 d })^2 \end{aligned}$ Using the square of a difference pattern: $\begin{aligned} &\phantom{=}({6 c })^2 - 2({6 c })({7 d })+({7 d })^2 \\\\ &=({6 c } - {7 d })^2 \end{aligned}$ In conclusion, $36 c ^2 - 84 c d + 49 d ^2=(6 c - 7 d )^2$ Remember that you can always check your factorization by expanding it.